This invention relates to methods of forming meltblown webs and in particular to methods of forming meltblown webs containing meltblown fibers and particulate material.
It has been desired to provide a method of forming particle-containing meltblown webs for a variety of purposes, wherein a predetermined amount of particles is held in the web while minimizing the amount of "dusting" (i.e., particles undesirably dropping out of the web) the web may suffer.
Various approaches to retaining particles within a web have been proposed. One such approach discloses a self-supporting durable flexible conformable low-pressuredrop porous sheet product that contains a uniform three-dimensional arrangement of discrete particles. The sheet product includes, in addition to the particles, a web of meltblown fibers in which the particles are uniformly dispersed. The particles are physically held, such as by mechanical entanglement, in the web even though there is only point contact between the meltblown fibers and the particles. ("Point contact" occurs when preformed bodies abut one another. It is distinguished from "area contact," such as results when a liquid material is deposited against a substrate, flows over the substrate, and then hardens in place.) Even though the particles are mechanically entangled within the interstices of the web, a portion of the particles still undesirably drop out of the web during handling.
Another approach discloses using adhesive polymers for forming the meltblown web. In addition to being physically entrapped in the web, the particles of this approach are also adhered to the surfaces of the meltblown fibers. Even though this may be viewed as an improvement over retaining particles within a web by point contact, this approach accomplishes its objective with the use of expensive adhesive polymers.
For the foregoing reasons, there is a need for an improved method of forming meltblown webs having particles substantially uniformly and homogeneously dispersed therethrough and retained therein by more than mere point contact or mechanical entanglement, wherein dusting is substantially eliminated without the addition of expensive adhesive polymers.